Display devices produced by using liquid crystalline compounds (the term "liquid crystalline compounds" is used in this specification as a general term for the compounds which exhibit a liquid crystal phase and for the compounds which do not exhibit a liquid crystal phase but are useful as component of liquid crystal compositions) have widely been utilized for the display of watches, tabletop calculators, word processors, or the likes. In recent years, researches on in-plane switching (IPS) mode and vertical alignment (VA) mode by which viewing angle can be improved at a moderate cost have extensively been conducted.
Among the liquid crystal compositions for IPS mode or VA mode, those having a negative dielectric anisotropy value are preferable, and further the compositions are sought having such physical properties as voltage holding ratio is high, threshold voltage is low, their dependency on temperature is small, temperature range of liquid crystal phase is wide, miscibility with other liquid crystal materials is excellent, and viscosity is low.
As the component for such liquid crystal compositions, many liquid crystalline compounds in which fluorine atom substituted at a lateral position were investigated, and the patents disclosing, for example, the following compounds are published: ##STR2##
However, compounds of the formula 1) are high in viscosity and low in voltage holding ratio since they have ester bond. Compounds of the formula 2) or 3) have problems such that the compounds readily exhibit smectic phase, and hardly form stable nematic phase when used as component of liquid crystal compositions, particularly at low temperatures.